FROMGIT: irqchip/git-v3-its: Implement irq_retrigger callback for device-triggered LPIs

It is pretty easy to provide a retrigger callback for the ITS,
as it we already have the required support in terms of
irq_set_irqchip_state().

Note that this only works for device-generated LPIs, and not
the GICv4 doorbells, which should never have to be retriggered
anyway.

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

Bug: 140053385
(cherry picked from commit 5f774f5e
 https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git

 irq/gic-retrigger)
Change-Id: I08b9f838e90aa56d04f3e65310e54e4d17e2ec9b
Signed-off-by: Eric Biggers <ebiggers@google.com>